Thymus gland

ANATOMY

• ANATOMY OR SYSTEM AFFECTED: Blood, cells, endocrine system, glands, immune system, lymphatic system
• SPECIALTIES AND RELATED FIELDS: Biochemistry, endocrinology, immunology, oncology DEFINITION: A gland that produces types of white blood cells for maintaining the immune system.
• DEFINITION: A gland that produces types of white blood cells for maintaining the immune system.

Structure and Functions

The thymus gland is a pinkish-gray organ that lies in front of the ascending aorta, beneath the top of the sternum. It consists of two lobes that are divided into lobules by a septum, or wall. Each thymic lobule contains lymphoid tissue organized into a densely packed outer layer called the cortex, a less-dense center called the medulla, and a thin covering around the outside of the thymus called the capsule. The thymus is relatively large in infants and typically grows to its maximum size around the age of two. After puberty, it gradually decreases in size until it blends in with the surrounding tissue.

The major cells of the thymus are morphologically indistinguishable from small, circulating lymphocytes. Lymphocytes (white blood cells) divide, differentiate, and mature in the thymic cortex to become T cells, a heterogeneous group of cells that are essential in protecting the body against infections that can be produced by invading foreign organisms. Once T cells mature, they migrate into the thymic medulla and eventually enter the bloodstream and travel to other lymphatic organs, where they bolster the immune system against disease. The thymus also produces a thymic hormone, thymosin, which is involved in T-cell development and immune regulation.

Disorders and Diseases

The thymus is critical in developing the immune system in children. If it malfunctions or is surgically removed, then a child has little to no ability to fight off disease. Signs and symptoms of thymus dysfunction include shortness of breath, facial swelling, muscle weakness, blurred vision, double vision, flushing, and neck pain and swelling. Myasthenia gravis, a neuromuscular disease that causes fluctuating muscle weakness, has been linked to thymus dysfunction. Proper diagnosis is critical so that appropriate treatment can be administered.

Although uncommon, thymic cancer can occur. Thymomas are generally slow-growing tumors that are most often found in middle-aged people. Previously, thymomas were characterized as benign (non-cancerous) or malignant (cancerous) tumors. However, recent research has caused challenges for doctors in their classification of thymomas, as evidence suggests that some thymomas have the potential to become cancerous over time.

A much rarer condition is thymic carcinoma, which develops more quickly than thymoma and is more likely to spread to other parts of the body. If a thymic tumor is found from images produced by chest X-rays, computed tomography (CT) scanning, or magnetic resonance imaging (MRI), then the tumor may be surgically removed or treated with radiation.

Perspective and Prospects

Early anatomical descriptions of the thymus date back to ancient Greek physicians such as Galen. The functions of the thymus were not well understood until the 1960s, when its role in the immune system was discovered. In 2007, it was reported that natural killer T (NKT) cells, a type of T cells that mature in the thymus, help regulate insulin-dependent diabetes mellitus. Research is focused on the development of NKT cell-based approaches for immunotherapeutic treatment of this disease. Research indicates that natural killer (NK) cells may impair thymus regeneration by damaging thymic epithelial cells, suggesting that regulating NK cell activity could improve immune recovery after injury.  Scientists can generate functional natural killer T (NKT) cells from stem cells using artificial thymic organoids, supporting advances in personalized immunotherapy. In addition, doctors are researching the structural and functional roles of thymic innervation, as neural regulation has gained recognition as a key factor in immune cell development and function. The central nervous system (CNS) in the brain plays a crucial role in coordinating immune responses, both through direct innervation via peripheral nerves and through neuroendocrine signaling. Research shows that certain regulatory T cells can return to the thymus and promote its regeneration by releasing growth factors such as amphiregulin, suggesting new possibilities for immune system repair therapies. Scientists are also working on reconstructing the thymus using stem cells and organoid models, which may eventually allow replacement of damaged thymic tissue and improve immune function in conditions such as aging, congenital absence, and cancer treatment.

Bibliography

Anastasiadis, Kyriakos, and Chandi Ratnatunga, editors. The Thymus Gland: Diagnosis and Surgical Management. Springer, 2007.

Carpenter, Randall S., et al. “Neural Regulation of the Thymus: Past, Current, and Future Perspectives.” Frontiers in Immunology, vol. 16, no. 1552979, 2025, doi.org/10.3389/fimmu.2025.1552979. Accessed 26 Mar. 2026.

Dabrowski, Marek P., and Barbara Dabrowska-Bernstein. Immunoregulatory Role of Thymus. CRC Press, 1989.

Lavini, Corrado, et al., editors. Thymus Gland Pathology: Clinical, Diagnostic, and Therapeutic Features. Springer, 2008.

"Myasthenia Gravis." MedlinePlus, US National Library of Medicine, 10 June 2024, medlineplus.gov/myastheniagravis.html. Accessed 26 Mar. 2026.

“Naturally Killing Thymus Regeneration.” Fred Hutchinson Cancer Center, 28 Jan. 2026, www.fredhutch.org/en/news/spotlight/2026/01/tst-granadier-natimmuno. Accessed 26. Mar. 2026.

“Researchers Discover Key to Boosting Thymus Regeneration after Damage.” News-Medical, 3 Feb. 2025, www.news-medical.net/news/20250203/Researchers-discover-key-to-boosting-thymus-regeneration-after-damage.aspx. Accessed 26. Mar. 2026.

“Thymus: The Function of the Gland & Why It Is Important.” Cleveland Clinic, 15 May 2022, my.clevelandclinic.org/health/body/23016-thymus. Accessed 26 Mar. 2026.

Wei, Yunpeng, and Yong Zhao. “De novo Thymus Reconstitution: The Rising of Cell-based Strategies.” International Journal of Immunology, vol. 13, no. 1, 2025, pp. 7–16, https://doi.org/10.11648/j.iji.20251301.12. Accessed 26. Mar. 2026.

“What Is Thymus Cancer?” American Cancer Society, 15 Jan. 2025, www.cancer.org/cancer/types/thymus-cancer/about/what-is-thymus-cancer. Accessed 26 Mar. 2026.